Technical Field
The present invention relates to phased array transceivers and, more particularly, to tapering in phased array systems to improve transmission and reception pattern characteristics.
Description of the Related Art
A phased array system uses an array of antenna elements for a single transmitter or receiver. By adjusting a phase shift between antenna elements, the gain of the entire array can be precisely directed during operation, making it possible to achieve high gains with pinpoint accuracy.
However, while the highest gain is focused on the main lobe of the array's emission pattern, side lobes may also exist. Side lobes represented waste in the potential gain of the antenna array, as gain that could be directed along the main lobe is instead oriented off to the side. In addition, side lobes create interference in undesired directions in transmitter mode and allow the reception of interfering signals from undesired directions in receiver mode.
In a phased array, the direction of the main lobe is set by the phase setting applied to each element. Tapering is used to control the side lobes by controlling the gain of an amplifier at each antenna element. Ideally, varying the gain at each element should not change the phase, otherwise the direction of the main lobe changes and/or sidelobes may be affected as well. Ideally, phase shifting in an element should not vary the gain. In practice, phase and gain adjustment are non-orthogonal, making calibration and tapering challenging. Variable gain amplifiers (VGAs) exhibit different phase for different gain settings and phase shifters typically show gain/loss variations with phase settings as well.
For these reasons, conventional systems determine a correct gain and phase iteratively, setting the gain and phase of antenna front-ends in turn until the desired overall gain and phase of the front-end is achieved. This decreases the responsiveness of the system and limits its ability to quickly adapt to changing needs. In addition, as the size and spatial resolution of the array increase, then the number of gain and phase settings needed increases in turn. For large systems, the memory demands can become impractical, particularly if they are deployed at small scale on an integrated circuit.